This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 00 16584 filed Dec. 19, 2000, the entire contents of which are incorporated by reference.
The invention relates to radiation equipment, such as X-ray radiation apparatus, and more particularly to a collimator intended for use in such apparatus.
In X-ray apparatus, radiation is emitted from one point on a source. The radiation takes the form of a cone directed towards an object to be examined or towards an X-ray sensitive sensorxe2x80x94for example a photographic plate or a digital sensing means. The cone generally has crosswise dimensions which are greater than the dimensions of the object to be examined or the sensitive means. The collimator is a device which is placed between the source and the object to be examined, allowing a part of the X-rays to be blocked off whereby radiation is only applied to the object to be examined inside an examination region or in the region corresponding to the sensor. The collimator is adjustable to allow different examinations.
Such a collimator is disclosed in U.S. Pat. No. 3,668,402. In that patent, the collimator is constituted by two web assemblies opaque to X-rays. Each web assembly has a pair of spaced and connected webs which form a continuous loop reaved over a pair of drums. The two assemblies are arranged one above the other, with the drums perpendicular to each other. The facing edges of the webs of one assembly define the facing edges of a rectangular opening through which X-rays can pass. The edges of the webs of the other assembly define the other two edges of the rectangular opening. The collimator is adjusted in order to vary aperture size by causing one of the assemblies to roll using the drums. The facing edges of the webs of an assembly are consequently brought closer together or further apart.
This collimator has the disadvantage of not making it possible to obtain an asymmetric aperture. Rotation of a web assembly causes simultaneous displacement in the opposite direction and through the same distance, of the facing edges of the collimator opening. The opening is consequently always symmetric with respect to an axis of the conical X-ray beam. Additionally, the collimator is larger than maximum aperture size. In a position of maximum collimator aperture, the edges of a given web overlap and the web extends between the pair of drums.
There is consequently a need for a collimator the aperture of which can be adjusted asymmetrically. Such an asymmetric aperture is notably useful for mammography. In effect, in such apparatus, it is difficult to readily move the organ to be examined and to ensure that it is systematically well positioned on the axis of the X-ray beam.
In an embodiment of the present invention, a collimator has four flexible shutters defining the edges of the collimator aperture. Each shutter can be moved independently of the other shutters.
In this structure, the position of each edge of the aperture can be adjusted independently. Using this collimator, an asymmetric aperture can be obtained. The collimator aperture can be adapted to the object or organ to be examined while limiting radiation outside the object or organ. It is not necessary for the object or organ to be placed directly on the axis of the X-ray beam.